This invention relates to fluid compositions useful especially for transmitting energy in mechanical systems and, more particularly, to water-based compositions useful in transmitting hydraulic energy having enhanced lubricity and anti-wear properties.
Water-based hydraulic fluids are well known and have been used commercially for a number of years especially in applications where fire resistance is desired. One commonly used class of such water-based fluids, as disclosed, for example, in U.S. Pat. No. 2,602,780 to Zisman et al. and U.S. Pat. No. 2,768,141 to Langer et al., contain water soluble glycols or glycol ethers for low temperature protection and a high molecular weight polymeric thickener such as water soluble poly(alkylene oxide) polymers for viscosity control. Such compositions also contain a variety of additives in "packages" that are added to enhance lubrication, corrosion protection, and other performance characteristics necessary for hydraulic devices and lubricants.
Water-based hydraulic fluids commonly have high nonflammability, good temperature stability, and a relatively low cost, but generally have poorer anti-wear characteristics than petroleum-based fluids. Fluids used in energy transmission systems must possess sufficient lubricity and mechanical stability to enable them to be used in the self-lubricated pumps, valves, etc. employed in commercial hydraulic systems. Good lubricating properties, especially good lubricity and film strength, are particularly important in reducing the wear of moving components of hydraulic systems where the clearance between frictional surfaces may be very small and pressures may be very high.
Heretofore, various attempts have been made to improve the lubricating properties and/or poor anti-wear properties of these fluids including, for example, modifying the poly(alkylene oxide) polymers generally added as viscosity control agents; incorporating additives such as conventional oil improvers, E.P. agents, corrosion inhibitors, and sequestering agents; and incorporating special water soluble additives such as the oxyalkylene adducts of polyamides disclosed in U.S. Pat. No. 3,992,312 to Genjida et al. However, none of these methods have been found to be completely effective, particularly where anti-wear resistance under high pressure conditions is desired, and the development of water-based fluids that would meet these requirements would be highly desirable. Moreover, it would also be desirable to provide energy transmitting fluids that contain more water than the 50 percent to which such known fluids are generally limited in commercial applications.